EFFECTS OF CARBON-DIOXIDE ON REACTIONS AT IRON ELECTRODES IN AQUEOUS SALT-SOLUTIONS

The title subject has been studied by stationary, transient, potentiodynamic and chronopotentiometric polarization measurements; by rotating disk experiments; and by corrosion rate determinations from weight loss, all at 25 degree C and ambient pressure. The main effect of CO//2 is to stimulate hydrogen evolution. Two cathodic polarization waves appear for this stimulated reaction. The first (lower) wave is ascribed to hydrogen evolution from H//2CO//3 (and HCO//3** minus ), limited by homogeneous production of this reactant from hydrated CO//2 in a reaction layer at the electrode. The second (higher) wave is ascribed to hydrogen evolution directly from hydrated CO//2 (and HCO//3** minus ), limited by diffusion of this reactant to the electrode. Except through accompanying pH changes, CO//2 does not affect the active anodic dissolution, the passivation (in sulfate solution) or the pitting (in chloride solution) of iron noticeably, but simulates the anodic dissolution of this metal in its intermediate prepassive state.